This invention relates to guidewires commonly used in the placement of catheters at various locations in a patient's body, such as in the cardiovascular system, e.g., balloon catheters and angiographic catheters. Such catheters may be too flexible to be advanced unsupported through the patient's vasculature and require a quidewire to support and guide the catheter into place.
Typically, a guidewire first is manipulated through the patient's vasculature to a desired location. The catheter, which has a lumen adapted to receive the guidewire, then is advanced over the guidewire to follow it to the desired location. One very common quidewire construction has an elongate, flexible helical coil having a proximal end and a distal end, the latter being inserted into the patient. An internal core wire typically extends through the coil, the proximal end of the core wire being attached to the proximal end of the coil. The internal core wire may be tapered at its distal end or may not extend fully to the distal end of the helical coil thus providing a segment of increased flexibility at the distal end of the guidewire. The more flexible distal segment is advantageous in that it is less likely to cause trauma to a blood vessel. Guidewires also commonly have a safety wire which extend within the coil from the proximal to the distal end. The safety wire prevents detachment of a segment of the coil, should such a segment break off within the body. In some guidewires used for cardiovascular purposes, the distal portion of the helical coil is J shaped to provide improved steerability of the guidewire into various branches of a blood vessel.
This invention in particular relates to a class of guidewires having an inner core wire that is movable longitudinally within the lumen of the helical coil. The movable core wire permits variability in the flexibility of the distal end of the guidewire. The core wire can be drawn proximally to provide increased flexibility in the distal end or can be advanced towards the distal end of the helical coil to increase the stiffness at the distal end. Variable flexibility enables the guidewire to be used in situations where it is important to be able to vary the tip configuration from a soft, flexible atraumatic configuration to a stiffer, more easily pushed configuration.
Movable core guidewires having a helical coil with a J shaped distal portion are sometimes used for cardiovascular applications. The movable core is advantageous over the fixed core for the J-shaped guidewires because the size of the curve on the distal portion can be adjusted by moving the core wire distally (to straighten out the J) or moving the core wire proximally (to reform the J). The ability to control the shape of the J-tip increases the facility by which the guidewire can be manipulated to select a desired blood vessel at branch points.
It is very important, for patient safety, that the distal tip of the movable core does not strike through the side of the guidewire through a pair of adjacent turns of the helical coil. The risk of such "strike through" is somewhat greater when the distal portion of the guidewire is disposed in a more sharply curved or tortuous blood vessel or body lumen. Additionally, when the guidewire is advanced into such difficult vasculature, it increases the frictional forces developed between the movable core tip and the inner surface of the helical coil thus making it more difficult to move the movable core wire through the helical coil and also reducing the physician's sensitivity to the feel of the movable core. It is among the general objects of the invention to provide an improved movable core guidewire which avoids the foregoing difficulties.